To improve responsiveness to a sudden load variation, a known switching power supply device amplifies a ripple component of a feedback voltage and controls an output based on a comparison between a ripple component of an amplified output and a reference voltage (refer to Japanese Laid-Open Patent Publication No. 2010-35316).
In another switching power supply device, current is supplied to a node to which a reference voltage is applied via a resistor. This adds a slope voltage to the reference voltage. An output voltage is controlled by inputting the added voltage and a feedback voltage to a comparator (refer to US 2005/00286269).
However, in a comparator type switching power supply device, when control is executed so that a lower limit of a feedback voltage becomes equal to a reference voltage, the feedback voltage includes a ripple component corresponding to the output voltage. Thus, the control is executed so that the reference voltage becomes equal to a lower limit of the ripple. The ripple component changes depending on operational conditions including circuit parameters such as an inductance value of a coil, input/output voltage, and transmission frequency. Accordingly, the ripple component of the output voltage shifts the average value of the output voltage, and accuracy of the output voltage may not be obtained.
When current flows to a node to which a reference voltage is applied, it may be necessary to arrange a buffer circuit having a low input impedance in a generation source of the reference voltage to keep the reference voltage constant. However, due to offset variations in the buffer circuit, the output reference voltage value may be deviated from the input voltage value. It may thus be difficult to obtain an accurate output voltage.